Biomedical subjects

R Hentschke

Publications and source records attributed to R Hentschke.

14 recordsLinked to original sources

PubMed2003

Computer simulation study on the swelling of a polyelectrolyte gel by a Stockmayer solvent.

The swelling of a model polyelectrolyte gel is studied via three-dimensional molecular dynamics simulations, taking into account the counterions and the solvent explicitly. Each network bead carries a charge q(*). The counterion charge is -q(*), and thus the total system is neutral. The solvent is modeled via a Stockmayer fluid, i.e., each solvent particle is a point dipole plus a Lennard-Jones interaction center. A "two-box--particle transfer" simulation method is applied to calculate the swelling ratio of the network as well as the counterion mobility. The swelling of the network shows a broad maximum as a function of q(*) at T(*)(r)=T(*)/T(*)(c)=1.05 and P(*)(r)=P(*)/P(*)(c)=1.0. Here, T(*)(c) and P(*)(c) are the critical temperature and the critical pressure of the pure Stockmayer solvent, respectively, with dipole moments given by mu(*2)=1.0, 2.0, 3.0, and 4.0. The residence time of the counterions is calculated, showing a strong coupling to the charged network beads (condensation) as q(*) increases. Additional simulations at three different charge strengths (i.e., q(*)=0.5, 3.5, and 8.6) illustrate the complicated swelling behavior of the network under supercritical and subcritical conditions.

Journal Article↗

PubMed2002

Swelling of model polymer networks with different cross-link densities: a computer simulation study.

The swelling of model polymer networks with different cross-link densities is studied via molecular dynamics simulation. During the simulation, the solvent particles, consisting of one interaction center or six interaction centers, respectively, are transferred between two coupled simulation boxes. The gel box includes both network and solvent particles, whereas the solvent box contains solvent only. The particle transfer is controlled by the solvent chemical potential difference in the two boxes, which is calculated via the Widom test particle method for the one-site solvent and via Rosenbluth sampling for the chainlike solvent. The equilibrium swelling ratio of the network as well as the solvent diffusion coefficient under subcritical and supercritical conditions are computed as functions of the network cross-link density for a wide range of temperatures and pressures. In addition, the simulated swelling behavior is compared to a Flory-Huggins-type theory, which yields qualitative agreement for the systems studied here.

Journal Article↗

PubMed2002

Computer simulation study on the swelling of a model polymer network by a chainlike solvent.

A molecular-dynamics-particle-transfer method was used to study the swelling of a model polymer network by a short chain solvent. The solvent chains were transferred depending on the difference between the solvent chemical potentials in the coupled simulation boxes, containing pure solvent and gel, respectively. The chemical potentials were computed via the Rosenbluth sampling method. The simulated swelling ratio of the network under subcritical and supercritical conditions is compared with the prediction of a modified Flory-Huggins theory. In addition, the chains exhibit markedly different structural and dynamic properties in the corresponding phases due to the constraint imposed by the network, which are discussed in detail.

Journal Article↗

PubMed2001

Swelling of a model polymer network by a one-site solvent: computer simulation and Flory-Huggins-like theory.

A molecular-dynamics-Widom test particle-simulation was used to investigate the swelling of a model polymer network in contact with a one-site solvent under subcritical and supercritical conditions. Particle motion is computed via molecular dynamics. Simultaneously, the solvent particle concentration is controlled by direct comparison of the chemical potentials in two reference systems (pure solvent and network including solvent), which are calculated using Widom's test particle method. The simulated swelling isotherms exhibit complex behavior: at the subcritical conditions considered here, the swelling ratio decreases with increasing pressure. At the intermediate supercritical temperatures the isotherms exhibit a peak, which disappears with the elevation of temperature. At high temperatures, the swelling ratio of the network increases monotonically with increasing pressure. The corresponding isobars also exhibit a maximum, which broadens and shifts to higher temperatures with increasing supercritical pressure. These results are in qualitative agreement with the prediction of a modified Flory-Huggins theory and with the results of known experiments. Furthermore, the self-diffusion coefficients of the solvent in the network and in its pure state are simulated. The solvent mobility in the network is significantly decreased because of the hindrance of network beads, but exhibits different behavior at subcritical in comparison to supercritical temperatures.

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PubMed1995